IE and Edge combined to account for 38.7% of the global user share -- a stand-in for the percentage of all desktop and notebook PCs that ran those browsers -- in May, according to U.S.-based analytics vendor Net Applications. May's number for IE was down 2.7 percentage points from April, the largest one-month decline since Computerworld began recording browser data in 2005.

In the last six months alone, IE -- a bucket into which Net Applications also throws in Windows 10's Edge -- has lost 11.4 percentage points, an unprecedented decline for any browser at any point in the last 11 years.

As recently as November 2015, IE accounted for more than half of the global browser user share.

At the same time, Google's Chrome reaped what Microsoft sowed, as the relative upstart -- Chrome debuted eight years ago -- added 3.9 percentage points to its share to close out May with 45.6%, within sniffing distance of the majority milestone.

If Chrome continues on the torrid growth of the last 12 months, it could break the 50% bar as early as August, a remarkable change of fortunes for both it and IE in less than a year.

Like IE, Mozilla's Firefox also lost user share in May, falling 1.2 percentage points to 8.9%, a place the open-source browser last occupied in May 2005. However, at that point it was on the upswing and chewing into Microsoft's then-dominant share of nearly 90%.

Failing a turn-around, Firefox's user share will slide to just 5% in little more than a year, slumping to the same level now held by Apple's Mac-only Safari.

The decline of IE and the concurrent rise of Chrome have been remarkable in the slow-changing browser market. Computerworld has pointed to Microsoft's August 2014 decision to force customers to upgrade to a newer version of IE as the trigger point. That was when Microsoft told most customers to migrate to IE11 if they wanted to continue receiving security patches. Staring at a requirement to change browsers, people instead rethought their vendor choice.

The result: Momentum passed to Chrome, which slowly gained ground in the first half of 2015 before accelerating in the second half.

But at the turn to 2016, when the decree finally came into effect, Chrome's growth exploded and IE's contraction deepened. In the five months of this year, Chrome has boosted its user share by 13.3 percentage points; IE + Edge has shed 9.9 points.

At the time of Microsoft's announcement, Gartner analyst Mike Silver called the move "huge," likely not knowing how prescient he would be. In August 2014, 64% of all Windows users were running IE; last month, just 43% of all Windows users relied on IE or Edge.

The introduction of Windows 10 was another contributor to IE's fall, as the new operating system demoted IE to a legacy role and promoted Edge as the replacement. But Windows 10 users, who now make up nearly 20% of all PC owners, have been hesitant, increasingly so, to adopt Edge: In May, fewer than three in every 10 Windows 10 users chose Edge. That number has been slowly declining -- it was two out of three in October -- since Windows 10's launch last year.

Other data sources mirrored Net Applications' data, and also showed a decline -- albeit less dramatic -- for IE + Edge. The Digital Analytics Program (DAP), which counts visits to more than 4,000 websites operated by the U.S. government, indicated a drop of 1.2 percentage points, to 20.2%, for Microsoft's browsers in May, and an increase of four-tenths of a point, to 43.9%, for Chrome.

DAP's traffic is predominantly domestic, although at times as much as 15% of the visitors access the sites from overseas. Data from DAP differs from Net Applications' because the former includes smartphone-based browsers, including Chrome on Android and Safari on iOS, which the latter does not.

Data: Net Applications

After Microsoft mandated that Windows customers upgrade their browser, IE steadily ceded momentum to Google's Chrome, which became the top dog in April and extended its lead in May.

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